The process of burning batch-loaded wood in ambient air at atmospheric conditions begins with the application of sufficient heat (greater than approximately 350° F. (177° C.)) to initiate a self-sustaining combustion process. Heating first causes moisture contained in the fuel to evaporate into the space in the immediate vicinity of where the fuel heating is taking place with subsequent dispersion into the atmosphere. As fuel moisture is depleted in the area of the fuel being heated, the organic components of the fuel, consisting of but not limited to such compounds as lignin, hemicellulose, and cellulose, begin to break down by way of a thermal process called pyrolysis. Pyrolysis includes both oxidation and reduction reactions initiated by the increasing temperature of the fuel. Virtually all of the formed and reformed chemical species produced by the pyrolysis process are organic species ranging from simple methane and formaldehyde to complex molecules such as benzo-a-pyrene and some notorious toxins like dioxins.
At the temperatures at which wood pyrolysis reactions take place (i.e., generally above 300° F. (149° C.)) virtually all of the pyrolysis reaction products leave a burning piece of wood in a gaseous phase. This means that, at atmospheric conditions, the pyrolysis products will migrate or disperse out of and away from the wood fuel being heated. As these gases, all of which are combustible, leave the surface of the fuel they mix with air and it's 20.9% oxygen content. At the mixing point where there are combustible gases within the range of flammability concentrations and there is adequate temperature, generally above 600° F. (316° C.), the pyrolysis product and air mixture will generate a self-sustaining combustion process usually observed as flaming.
If the pyrolysis-product gases are too rich, become too diluted by air, or there is inadequate temperature to initiate a self-sustaining combustion process the pyrolysis-product gases will not “burn” and they will leave the combustion zone either as gaseous pollutants or as condensation droplets or aerosols which make up what is generally referred to as smoke or particulate emissions. If the pyrolysis products are only partially combusted as they leave the wood, carbon monoxide and solid particulate carbon particles known as soot are formed. When these incompletely combusted liquids and solids condense and are deposited on inner chimney walls the resulting formations are called creosote.
If excessive dilution takes place in the combustion zone, the concentration of those pyrolysis-product compounds that typically produce smoke particles in flue gases can be reduced to levels below their condensation vapor pressures. When this occurs, little or no smoke is observed in the flue gases. Even though concentrations may get diluted to levels below their respective condensation vapor pressures, the total mass of emitted materials remains in the flue gases.
Since the elemental makeup of wood consists primarily of carbon, hydrogen, and oxygen, the complete combustion of wood and it's pyrolysis products consists nominally of carbon dioxide and water. Small amounts of nitrogen and sulfur are present in wood at tenth of a percent levels and form nitrous oxides and sulfur oxides respectively when wood is burned. Other inorganic constituents of wood include the salts of calcium, sodium, potassium, magnesium, iron, silicon, chlorine, and phosphorus, which comprise virtually the total make up of the ash materials left after complete wood combustion has taken place.
To accomplish the compete combustion of wood it would first be necessary to heat the fuel evenly throughout and then as the various species of gaseous pyrolysis products are produced they would be evenly mixed with the appropriate amounts of air for ideal combustion and then evenly heated further to the appropriate temperature for initiating combustion (i.e., ignition temperature). This complete or ideal combustion process requires an ideal set of conditions that do not occur under the natural conditions found in fireplace combustion chambers. Under normal and typical fireplace conditions pieces of wood are being heated unevenly with some areas reaching temperatures adequate to initiate pyrolysis but not hot enough or uniform enough to generate enough combustible gas to initiate combustion. Because fuel heating in a fireplace is so uneven throughout the burning of a fuel load, there will always be zones, like near where flaming is occurring, where temperatures are hot enough to cause the production of pyrolysis products but not hot enough to cause them to burn or they become too dilute by mixing with air to burn. In either case, there are pyrolysis products, products of incomplete combustion (PICs), escaping the combustion zone and, if there are no further steps taken to combust these materials, they become pollutants discharged to the atmosphere.
Thus, there is a need for a method and apparatus to reduce or eliminate the products of incomplete combustion of wood in a fireplace. Presently known art attempts to address this problem, but has not completely solved the problem. The following represents a list of known related art:
Reference:Issued to:Date of Issue:U.S. Pat. No. 6,237,587Sparling et al.May 29, 2001U.S. Pat. No. 5,499,622WoodsMar. 19, 1996U.S. Pat. No. 6,227,194Barudi et al.May 8, 2001U.S. Pat. No. 4,249,509SymeFeb. 10, 1981U.S. Pat. No. 3,496,890La RueFeb. 24, 1970U.S. Pat. No. 4,422,437HirscheyDec. 27, 1983U.S. Pat. No. 5,460,511GrahnOct. 24, 1995
The teachings of each of the above-listed citations (which does not itself incorporate essential material by reference) are herein incorporated by reference. None of the above inventions and patents, taken either singularly or in combination, is seen to describe the instant invention as claimed.
Thus, while the foregoing body of art indicates it to be well known to have a fireplace afterburner, the art described above does not teach or suggest a fireplace afterburner which has the following combination of desirable features: (1) adjustable to fit in different sizes of fireplace; (2) adjustable for utilizing different fuel-gas including natural gas, propane, butane, or any mixture of fuel gases; (3) can utilize many catalytic materials that can enhance the oxidation of organic molecules in air; (4) can reduce wood-burning pollutant emissions, PICs, without utilizing catalytically-active materials; (5) can utilize different kinds of catalyst substrate (e.g., metal or ceramic) suitable for withstanding temperatures of up to 2300° F. (1260° C.) and different shape (e.g., honeycomb or reticulated foam) suitable for allowing the amount of flue-gas flow needed to prevent smoke spillage out the front of the fireplace on which it is installed; (6) when used with catalytically active materials, raises the temperature of fireplace flue gases (i.e., the total flue-gas stream) to at least 1501° F. (816° C.) which is the temperature at which some of the wood-burning pyrolysis products begin to oxidize to carbon dioxide and water; (7) can use either “natural” draft (i.e., the rising of heated gases in a duct) or induced draft (i.e., mechanically-assisted by a fan) to produce the flow of air and combustion gases through a chimney system duct necessary for maintaining proper fireplace operations and the exhaust of flue-gases to the atmosphere; (8) can be equipped with a catalyst-bed bypass to facilitate flue-gas flow during initial startup heating and to alleviate possible blockage of the catalyst; (9) can be equipped with an automatic catalyst bed temperature controller for maintaining minimum catalyst temperatures or preventing excessive temperatures that may be generated within the system during fireplace operation; (10) can be equipped with an electronic temperature sensor placed within the catalyst bed which can send a signal to an electrical-mechanical device which allows for moderating the heating source (i.e., increasing or decreasing the fuel-gas supply or electrical power source) within the minimum and maximum operating temperature range; (11) can be equipped with an emergency shut-down (i.e., failsafe) system that would turn off all fuel-gas flow or electrical power if excessive temperatures are reached or the operator detects a malfunctioning system.